Hen has necrotic looking hole under vent, pics What is this?

[cluckyclucky]

I have a hen of unknown age and breed that was given to me 3 weeks ago with 5 others. I noticed a week ago she was not as fast as the others and two days ago she started holding her neck very close to her body as though she was cold. I noticed her bottom was quite poopy so gave her a warm bath and found a necrotic looking hole underneath her vent. I cannot pull the scab off off as it is quite deep, especially in the middle. I did not see any traces of worms or eggs or maggots back there, but there is whitish/yellowish puss beside the hole.
She is still eating and drinking. Poops normal. Does anyone know what this is?

 

[emmaie892000]

It looks like flystrike other than the fact that you see no maggots or eggs. Perhaps something attacked her.
Flystrike often occurs in that area in particular. However, even if it isn't, you can treat it about the same. Because it's so close to her vent, you'll have to be careful to keep it clean. You may want an antibiotic, either injectable, to put in food/water, or as a wash for the hole itself. If you look at puncture wound threads, or flystrike threads, you'll find recommendations for medicine, and most are found in Tractor Supply or other feed stores. You'll want to keep her separated to make sure no others pick at her wound. The fact that she's eating, drinking, and pooping normally are all good signs. Just keep and eye on her, and try to reduce infection as much as possible (the pus sounds like it may already be a bit infected).